1. Field of the Invention
This invention relates to antimony/Lewis base adducts useful as source reagents for applications including Sb-ion implantation and formation of antimonide films.
2. Description of the Related Art
In the fabrication of advanced semiconductor devices, processes such as III-V MOCVD and p/n doping by ion implantation ideally require the use of Group III and Group V hydrides.
However, the hydrides of the heavier elements of Group III and Group V are unstable or in some cases are simply not known. For instance, stibine is only stable at very low temperatures (-78.degree. C.), decomposing spontaneously at room temperature, while indane cannot be isolated.
In addition, alkyl or aryl metal hydrides such as HSbR.sub.2 and H.sub.2 SbR, wherein R is alkyl, are also unstable.
Although literature reports indicate that researchers have synthesized and used metal hydrides as precursors when stored at low temperatures, widespread commercialization has not been possible due to the limited stability of the hydrides to light, heat and metal surfaces (i.e., stainless steel). Sophisticated microelectronic components and device heterostructures are driving the development of CVD precursors that exhibit useful volatility and the ability to deposit high-purity films. Currently, many III-V devices based upon strained layer superlattices and multiple quantum wells (MQW) are fabricated by molecular beam epitaxy (MBE). MBE is relatively slow and expensive when compared to alternate thin-film growth techniques used for microelectronics.
Although chemical vapor deposition (CVD) offers a low-cost, high throughput approach to device manufacturing, a lack of suitable, low temperature CVD precursors has hindered its widespread applicability. This is particularly true for Sb-based heterostructures that display important optoelectronic and electronic properties, including InSb, InGaSb, InAsSb, GaAlSb and InSbBi. Volatile and thermally stable Sb precursors would facilitate the chemical vapor deposition of antimonide thin-films, as required for the large scale, controlled production of antimonide based lasers, detectors and microelectronic sensors.
Antimonide materials are attractive for commercial infrared optoelectronic applications. The compositional variety and stoichiometry of III-V compound semiconductors allows for nearly complete coverage of the infrared spectrum. Bandgaps ranging from 2.5 eV in AlP to 0.2 eV in InSb can be achieved by forming strained thin-films with the proper elemental and stoichiometric compositions. Materials of greatest interest include InSbBi and InAs-SbBi for long wavelength (8-12 mm) infrared detectors, InAsSb and InGaSbfor mid-infrared absorbers in military applications, and InSb/In.sub.1-x Al.sub.x Sb light emitting diodes (LEDs) for mid-infrared chemical sensor applications. Many of these materials, however, as mentioned above are metastable compositions that necessitate high-purity films and low processing temperatures.
Antimonides are also of great interest as semiconductor infrared lasers. For instance, a type-II quantum well superlattice laser, comprised of InAsSb active layer with alternating InPSb and AlAsSb cladding layers, provides 3.5 mm emission upon electron injection. Similarly, mid-infrared lasers comprised of InAs/InGaSb/InAs active regions with lattice-matching to AlSb cladding layers were also demonstrated. The device fabrication requires thin-film processing of elemental aluminum, antimony, gallium and indium to produce both the active and cladding layers, and thereby, presents a significant technological challenge. The inherent physical properties of Ga, Sb and In necessitate low processing temperatures to alleviate inter-diffusion, melting, and re-evaporation (i.e., InSb melts at 525.degree. C.). Unfortunately, current Sb CVD sources, such as trimethyl antimony, require processing temperatures in excess of 460.degree. C. to achieve precursor decomposition and useful film growth rates.
Additionally, if advances in DRAM storage density based upon current technology are to continue, it will be necessary to develop dopants that can be utilized in very shallow p/n layers. This implies that traditional dopants such as boron (p-type) and phosphorus (n-type) will have to be replaced due to their high mobility in silicon (which results in a breakdown of the junction, even with reduced thermal budgets).
Of further concern is the lack of accurate control of the implant profile obtained by using B and P. High implantation energies are utilized for these implant species since lower beam energies are difficult to achieve, as a result of beam instabilities and low beam currents characteristically obtained at lower energy conditions.
Given the fact that more massive fragments that may be used in ion implantation applications (such as BF.sub.2.sup.+) also have deleterious consequences on device performance, it has become increasingly apparent that alternative dopants are required.
The two logical choices for p- and n-type dopants are indium and antimony, respectively, due to their greater size and mass, which provide superior diffusion characteristics relative to traditional implant species. These properties make it is possible to use lower implant energies and more advantageous geometries when depositing the shallow p/n junctions that are critical to DRAM storage density increases. However, as mentioned previously herein, suitable volatile antimony and indium precursors are currently unavailable.